13C及29Si核磁共振研究苯乙烯-二甲基硅氧烷嵌段共聚物的弛豫及分子运动

用¹³C及²⁹Si核磁共振研究了苯乙烯(S)及二甲基硅氧烷(Si)嵌段共聚物中硅氧烷软段的固体及溶液谱的自旋-晶格弛豫时间T₁。固态嵌段共聚物主链²⁹Si及侧甲基¹³C的T₁都与均聚物的T₁相近,但在CdCl₃溶液中各种嵌段共聚物的T₁与均聚硅氧烷相差颇大。用偶极-偶极相互作用来解释高聚物的自旋-晶格弛豫。苯乙烯-二甲基硅氧烷嵌段共聚物具两相结构,所以嵌段共聚物中软段及硬段微区中链段的运动与在均聚物分子中链段的运动模式基本相同。而CdCl₃对聚苯乙烯或聚硅氧烷都是良溶剂,软段硬段之间有相互影响。所以其链段运动与均聚物不同,从而导致链段运动的相关时间τ_c变短和T₁的增长。

A STUDY ON THE RELAXATION AND MOLECULAR MOTION OF STYRENE-DIMETHYL SILOXANE BLOCK COPOLYMERS BY 13C AND 29Si SPECTROSCOPY

The solid and solution spectra of the soft segment of styrene-dimethyl sil-oxane block copolymeri, are studied by ¹³C and ²⁹Si NMR spectroscopy and their spin-lattice relaxation times(T₁) are determined.It is found that in CDCl₃ solution the T₁s of the main chain ²⁹Si and the pendant methyl group ¹³C are toth longer than the homopoly dimethylsiloxane, but they are identical with the homopolymer in the bulk state,It is known that the spin-lattice relaxation of high polymers is mainly dominated by dipole-dipole interactions. There isa clear two-phase strucre, Therefore, the mode of motion is essentially the same in block and in homopolymers CDCl₃ is a good solvent for polystyrene and polydimethylsiloxane. In CDCl₃ solution there is a mutual effect between the hard and the soft segmental motion no longer resembles that of the homopolymer.Therefore, the correlation time of the segmental motion of the block copolymer is shorter and T₁ is much longer.